"This was not a case of bias," the Svea court of appeals said in a statement.

Lawyers for the four men had appealed the Stockholm district court's April 17 guilty verdict and demanded a retrial after it emerged that one of the judges, Tomas Norstroem, belongs to several copyright protection associations where film and record industry officials are also members.

The judge should have informed the court of his affiliations early on in the proceedings, the court said.

"The fact that he failed to shed light on this does not however mean that there was any wrongdoing during the proceedings that would require a retrial," it said.

Stockholm's district court sentenced Fredrik Neij, Gottfrid Svartholm, Peter Sunde and Carl Lundstroem each to a year in jail and ordered them to pay damages of 30 million kronor (2.72 million euros, 3.56 million dollars) to the movie and recording industry.

Norstroem is a member of the Swedish Copyright Association, as are Monique Wadsted, who represented the film and recording industry in the trial, and the head of the Swedish Anti-Piracy Agency, Henrik Ponten.

The judge also sits on the board of the Swedish Association for the Protection of Industrial Property.

Norstroem refused to comment on the appeals court findings on Thursday. In April he insisted he was not biased.

"I do not consider myself biased because of these affiliations," he said at the time.

Founded in 2003, The Pirate Bay makes it possible to skirt copyright fees and share music, film and computer game files using bit torrent technology, or peer-to-peer links offered on the site.

None of the material can be found on The Pirate Bay server itself.

The Pirate Bay claims to have some 22 million users worldwide.

The date for the appeals trial is yet to be set.

(c) 2009 AFP